Bone screws are commonly used to fix adjacent bones or bone fragments with respect to each other, or to attach structure to bone. For example, bone screws are commonly used to help repair fractures in bone, to attach bone plates to bone, to fix adjacent vertebral bodies, and so on.
However, typical bone screws and conventional methods of bone screw insertion can introduce undesirable complications in such procedures. For example, conventional methods of bone screw insertion can lead to: small and/or mobile bone fragments dislocating from the bone or bone segment due to axial pressure and insertion torque transmission during screw insertion; screw loss during operation (including transporting the screw from its storage place to final fixation location in the patient); shear off and cam out of the screw head during screw insertion and/or removal; slipping between the screw driver interface and the screw driver; stripping of the screw driver interface; bone milling during rotational insertion of self drilling and/or self tapping screws; misalignment of the pre-drilled holes in adjacent bone fragments and/or bone plates which can lead to secondary dislocation and inaccurate positioning of the bone fragments and/or bone plate; suboptimal screw fixation due to angular misalignment of a pre-drilled pilot hole's axis and the desirable screw insertion axis; and post operative back out of screws. Furthermore, when conventional bone screws are used to attach small bone segments that have little structural support, the axial and rotational force required to start a screw into such small fragments can be such that the fragment becomes dislocated. Additionally, when it is desirable to use a long bone screw, driving the screw into bone can become laborious.
Additional complications of using typical bone screws and conventional methods of bone screw insertion can be introduced by the sheer number of steps, and associated opportunities to introduce errors, required in a given procedure. For instance, in the case of a bone fracture, FIG. 1A illustrates a conventional bone lag screw 10 with a partially threaded shaft that is used to join two fractured bone segments 11a and 11b. Unfortunately, performing this procedure with the use of conventional bone screws is complex and involves a number of steps. First, the surgeon reduces the fracture, and then drills a first hole 12 into the first bone segment 11a, such that the first hole 12 has a diameter 1 equal to the major diameter of the screw 10. Next, the surgeon inserts a drill guide into the hole 12 and then drills a second hole 13 having a diameter 2 that is equal to the minor diameter of the screw 10. Once the two holes are drilled, the bone is countersunk for the head of the screw 10, the depth of the holes are measured to determine the length of screw needed, and finally the screw is inserted and threads 14 of the screw 10 are tightened into the second hole 13. FIG. 1B illustrates a procedure for similarly attaching a bone plate 11c to a bone segment 11d using a conventional bone screw 10 with a fully threaded shaft.